Method of preparing light-sensitive silver halide emulsions and dispersions of photographically useful compounds

Method of preparing light-sensitive silver halide emulsions by the following steps:

• a. precipitating in aqueous silica medium silver halide by reaction of an aqueous silver salt solution and an aqueous halide solution in aqueous colloidal silica medium wherein said aqueous silica is the sole protective colloid present;
• b. lowering the pH of the said medium to a value of 1.0 to 4.0.
• c. adding to the said medium hydroxy ethyl cellulose as a hydrogen bridge forming polymer flocculating agent so that aggregates are formed;
• d. removing the clear supernatant liquid formed containing water-soluble salts by means of a siphon or by decanting;
• e. concentrating the emulsion during precipitation by dialysis or ultrafiltration or after precipitation by dialysis or ultrafiltration or by flocculation and decantation, followed by washing and further decantation;
• f. readjusting the pH to a value of 1.0 to 4.0;
• g. removing the clear supernatant liquid;
• h. repeating procedure e to g if flocculation and decantation are applied;
• i. causing redispersion of the flocculate by adding an excess of said aqueous colloidal silica or a hydrogen-bridge forming polymer except for gelatin and stirring the redispersed flocculate.

Method of preparing dispersions of compounds having at least one photographically useful group by the following steps:

• a. precipitating in aqueous silica medium photographically useful compound in a non-watersoluble but alkali-soluble aqueous alkaline solution, whether or not in the presence of a non-aqueous solvent, by lowering the pH of the solution to a value of 1 to 4 in the presence of at least one cellulose derivative as a hydrogen bridge forming polymer flocculating agent in a dispersion vessel so that aggregates are formed;
• b. removing the clear supernatant liquid containing water-soluble salts by means of a siphon or by decanting;
• c. concentrating the dispersion during the precipitation by dialysis or ultrafiltration or after precipitation by dialysis or ultrafiltration or by flocculation and decantation, followed by washing and further decantation;
• d. removing the clear supernatant liquid;
• e. repeating procedure c to d if flocculation and decantation is applied;
• f. causing redispersion of the flocculate by adding an excess of said aqueous colloidal silica or a hydrogen-bridge forming polymer except for gelatin and stirring the redispersed flocculate.